U.S. patent application number 13/835873 was filed with the patent office on 2013-08-15 for bit patterned media.
This patent application is currently assigned to SEAGATE TECHNOLOGY, LLC. The applicant listed for this patent is Seagate Technology, LLC. Invention is credited to Eric Freeman, Jim Hennessey, David S. Kuo, Kim Yang Lee, Mark Ostrowski, Bing K. YEN.
Application Number | 20130208378 13/835873 |
Document ID | / |
Family ID | 41799561 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130208378 |
Kind Code |
A1 |
YEN; Bing K. ; et
al. |
August 15, 2013 |
BIT PATTERNED MEDIA
Abstract
The invention relates to bit patterned recording media having a
stop layer for chemical mechanical polishing. One embodiment of the
present invention is a method of manufacturing a magnetic recording
medium comprising the step of planarizing by chemical mechanical
polishing until the stop layer is reached. The present invention
also provides a magnetic recording medium having a stop layer.
Inventors: |
YEN; Bing K.; (Cupertino,
CA) ; Hennessey; Jim; (Campbell, CA) ;
Freeman; Eric; (Oakland, CA) ; Lee; Kim Yang;
(Fremont, CA) ; Kuo; David S.; (Palo Alto, CA)
; Ostrowski; Mark; (Lakeville, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seagate Technology, LLC; |
|
|
US |
|
|
Assignee: |
SEAGATE TECHNOLOGY, LLC
Cupertino
CA
|
Family ID: |
41799561 |
Appl. No.: |
13/835873 |
Filed: |
March 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12208095 |
Sep 10, 2008 |
8435654 |
|
|
13835873 |
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Current U.S.
Class: |
360/135 ;
216/22 |
Current CPC
Class: |
G11B 5/82 20130101; G11B
5/84 20130101; B82Y 10/00 20130101; G11B 5/855 20130101; G11B 5/743
20130101 |
Class at
Publication: |
360/135 ;
216/22 |
International
Class: |
G11B 5/84 20060101
G11B005/84 |
Claims
1-10. (canceled)
11. A method of manufacturing a magnetic recording medium
comprising: forming a magnetic layer upon a substrate, the magnetic
layer comprising an array of discrete magnetic bits separated by a
non-magnetic filler material; depositing a stop layer upon the
magnetic layer; depositing an excess layer upon the stop layer; and
planarizing by chemical mechanical polishing until the stop layer
is reached.
12. The method of claim 11, wherein the filler material is selected
from Ah03, Si0.sub.2, SiO.sub.xN.sub.y, and combinations
thereof.
13. The method of claim 11, wherein the filler material comprises
Ah03.
14. The method of claim 11, wherein the stop layer is selected from
carbon, platinum, gold, chromium, ruthenium, diamond, tungsten,
SiC, SiO.sub.xN.sub.y, NiCu, and combinations thereof.
15. The method of claim 11, wherein the stop layer comprises
carbon.
16. The method of claim 11, wherein the excess layer comprises
Ah03.
17. The method of claim 11, wherein the stop layer has a thickness
of about 2 to about 200 nm.
18. The method of claim 17, wherein the stop layer has a thickness
of about 2 to about 10 nm.
19. The method of claim 11, wherein the step of planarizing by
chemical mechanical polishing comprises measuring an increase in
induced polishing friction to determine the stop layer has been
reached.
20. The method of claim 11, wherein the step of planarizing by
chemical mechanical polishing comprises measuring changes in
surface optical reflectivities to determine the stop layer has been
reached.
21. The method of claim 11, wherein the step of planarizing by
chemical mechanical polishing comprises measuring changes in
electrical currents to determine the stop layer has been
reached.
22. A magnetic recording medium, comprising: a substrate; an array
of discrete magnetic bits on the substrate, wherein the magnetic
bits have a width defined by a distance between a first side
surface and a second side surface; regions of a non-magnetic filler
material between the discrete magnetic bits in the array; an
overlying layer in direct contact with the magnetic bits; and a
stop layer between the regions of non-magnetic filler material and
the overlying layer, wherein the stop layer is adjacent to the
first and the second side surfaces of the magnetic bits.
23. The magnetic recording medium of claim 22, wherein the magnetic
bits in the array have a thickness defined by a distance between a
first surface thereof in direct contact with the substrate and a
second surface thereof in direct contact with the overlying layer,
and wherein a combined thickness of the non-magnetic filler
material between the bits and the stop layer adjacent the bits is
substantially equal to not greater than a thickness of the
bits.
24. The magnetic recording medium of claim 22, wherein the CMP
removal rate selectivity of the stop layer is at least about 80
times the CMP removal rate selectivity of either of the magnetic
bits or the non-magnetic filler material.
25. The magnetic recording medium of claim 22, wherein the
overlying layer comprises one or more cap layers and lubricant
layers.
26. A magnetic recording medium, comprising: a substrate; an array
of discrete magnetic bits on the substrate, wherein the magnetic
bits have a width defined by a distance between a first side
surface and a second side surface, and wherein the magnetic bits
have an exposed top surface; regions of a non-magnetic filler
material between the discrete magnetic bits in the array; and a
discontinuous stop layer overlying the regions of non-magnetic
filler material, wherein the stop layer abuts the first and the
second side surfaces of the magnetic bits in the array, and wherein
herein the stop layer comprises an array of apertures occupied by
the magnetic bits in the array.
27. The magnetic recording medium of claim 1, wherein a combined
thickness of the non-magnetic filler material and the stop layer is
substantially equal to a thickness of the magnetic bits in the
array.
Description
BACKGROUND
[0001] Magnetic recording media are widely used in various
applications, e.g., in hard disk form, particularly in the computer
industry, for storage and retrieval of large amounts of
data/information. These recording media are conventionally
fabricated in thin film form and are generally classified as
"longitudinal" or "perpendicular", depending upon the orientation
(i.e., parallel or perpendicular) of the magnetic domains of the
grains of the magnetic material constituting the active magnetic
recording layer, relative to the surface of the layer.
[0002] In the operation of magnetic media, the magnetic layer is
locally magnetized by a write transducer or write head to record
and store data/information. The write transducer creates a highly
concentrated magnetic field which alternates direction based on the
bits of information being stored. When the local magnetic field
applied by the write transducer is greater than the coercivity of
the recording medium layer, then the grains of the polycrystalline
magnetic layer at that location are magnetized. The grains retain
their magnetization after the magnetic field applied by the write
transducer is removed. The direction of the magnetization matches
the direction of the applied magnetic field. The pattern of
magnetization of the recording medium can subsequently produce an
electrical response in a read transducer, allowing the stored
medium to be read.
[0003] In conventional hard disk drives, data is stored in terms of
bits along the data tracks. In operation, the disk is rotated at a
relatively high speed, and the magnetic head assembly is mounted on
the end of a support or actuator arm, which radially positions the
head on the disk surface. By moving the actuator arm, the magnetic
head assembly is moved radially on the disk surface between
tracks.
[0004] Lithographically patterned media, also known as
bit-patterned media, are being pursued to increase areal recording
density as compared to conventional recording media. Bit-patterning
combines several hundred media grains into one single magnetic
island, which does not require large coercivities. The
manufacturing of lithographically patterned media typically
involves using photolithography techniques to form a pattern of
discrete and separated magnetic regions. This may include a
nanoimprint process, i.e., the stamping of soft resist materials
with hard stampers to mold a pattern within the resist.
[0005] As the size and spacing of magnetic device features have
decreased to increase recording density, the height of the steps of
these features have increased. Also, as the number of layers
deposited during the manufacture of magnetic devices increases,
irregularities in the surface of the layers increases. As a result,
chemical mechanical polishing (CMP) may be used to planarize
feature surfaces during processing.
[0006] CMP is used to remove surface topography in order to achieve
planar surfaces suitable for photolithographic patterning of
complex patterns. Material is removed during a CMP process by a
combination of chemical etching and mechanical abrasion. CMP
processes typically have a material removal rate of 300 to 500
nanometers (nm) per minute under normal process conditions. Removal
continues until an endpoint is reached, which is theoretically the
point where all of the excess material is removed, and a smooth
planar surface remains.
[0007] The CMP endpoint may be determined by a variety of
techniques. For example, prior CMP processes have incorporated
instruments to measure changes in the surface optical reflectivity,
changes in the surface temperature, and changes in eddy currents
induced through the layers. Other CMP processes alternatively use
prior test runs to estimate polish time to the endpoint. However,
these prior CMP endpoint detection techniques are subject to
variations as to when the endpoints are detected. Thus, there is a
need in the industry for a process capable of accurately detecting
CMP endpoints for fabricating consistent and accurate features in
bit-patterned media.
SUMMARY
[0008] The present invention relates to bit patterned recording
media having a stop layer for chemical mechanical polishing.
[0009] One embodiment of the invention is magnetic recording medium
having a substrate; a magnetic layer supported by the substrate,
where the magnetic layer has an array of discrete magnetic bits
separated by a non-magnetic filler material; and a stop layer for
chemical mechanical polishing. In another variation, the magnetic
recording medium further includes one or more cap layers and/or
lubricant layers.
[0010] According to another variation, the stop layer is disposed
between the discrete magnetic bits. In another variation, the stop
layer has a thickness of about 2 to about 200 nm, preferably about
2 to about 10 nm.
[0011] According to yet another variation, the filler material is
selected from Al.sub.2O.sub.3, SiO.sub.2, SiO.sub.xN.sub.y, and
combinations thereof, preferably Al.sub.2O.sub.3. In another
variation, the stop layer is selected from carbon, platinum, gold,
chromium, ruthenium, diamond, tungsten, SiC, SiO.sub.xN.sub.y,
NiCu, and combinations thereof, preferably carbon. In one preferred
embodiment, the filler material is Al.sub.2O.sub.3 and the stop
layer is carbon.
[0012] Another embodiment of the present invention is a method of
manufacturing a magnetic recording medium including the steps of
(a) forming a magnetic layer upon a substrate, the magnetic layer
having an array of discrete magnetic bits separated by a
non-magnetic filler material; (b) depositing a stop layer upon the
magnetic layer; (c) depositing an excess layer upon the stop layer;
and (d) planarizing by chemical mechanical polishing until the stop
layer is reached.
[0013] According to one variation, the excess layer comprises
Al.sub.2O.sub.3.
[0014] According to another variation, the step of planarizing by
chemical mechanical polishing includes measuring an increase in
induced polishing friction to determine the stop layer has been
reached.
[0015] In another variation, the step of planarizing by chemical
mechanical polishing comprises measuring changes in surface optical
reflectivities to determine the stop layer has been reached.
[0016] In yet another variation, the step of planarizing by
chemical mechanical polishing comprises measuring changes in
electrical currents to determine the stop layer has been
reached.
[0017] Additional advantages of this invention will become readily
apparent to those skilled in this art from the following detailed
description, wherein only the preferred embodiments of the
invention are shown and described, by way of illustration of the
best mode contemplated for carrying out the invention. As will be
realized, this invention is capable of other and different
embodiments, and its details are capable of modifications in
various obvious respects, all without departing from the invention.
Accordingly, the drawings and description are to be regarded as
illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a sectional view of a magnetic recording medium
according to one embodiment of the present invention.
[0019] FIGS. 2A-2G are sectional views illustrating the steps of a
method of manufacturing a magnetic recording medium according to
one embodiment of the present invention.
DETAILED DESCRIPTION
[0020] As used herein "substrate" refers to one or more layers that
provide a surface suitable for the formation of a bit-patterned
magnetic layer thereupon in the manufacture of a magnetic recording
medium. The substrate may comprise one or more different
materials.
[0021] FIG. 1 is a sectional view depicting a portion 7 of a
magnetic recording medium according to one embodiment of the
present invention, which includes substrate 8, optional overlying
layer(s) 9, and magnetic layer 10. Underlying substrate 8 is the
portion of the magnetic recording medium that is formed prior to
magnetic layer 10, and includes top surface 8a, upon which magnetic
layer 10 is formed. Optional overlying layer(s) 9 is the portion of
the magnetic recording medium that is disposed on top of magnetic
layer 10, after magnetic layer 10 is formed and planarized.
Underlying substrate 8 and overlying layer(s) 9 may provide a
variety of characteristics for the magnetic recording medium, such
as additional magnetic properties, magnetic isolation, or
protection.
[0022] Magnetic layer 10 includes an array of discrete magnetic
bits 12 (represented singularly in FIG. 1), non-magnetic filler
material 14, and stop layer 16, where stop layer 16 is used to
detect a chemical mechanical polishing (CMP) endpoint. Through the
use of stop layer 16, target thickness of magnetic layer 10 is
accurately controlled, and within wafer non-uniformity (WIWNU) is
improved.
[0023] Magnetic bit 12 is the portion of magnetic layer 10 that
provides magnetic properties, and exists in a region dimensionally
defined by surfaces 12a-12d. Surfaces 12b, 12d are disposed
adjacent to filler material 14. While surfaces 12a-12d depict
magnetic portion 12 as rectangular, magnetic bit 12 may
alternatively be other shapes, such as trapezoidal. Magnetic bit 12
is derived of one or more high-magnetic-moment materials, such as a
magnetic alloy. Examples of suitable magnetic alloys include iron,
cobalt, nickel, and combinations thereof. Examples of suitable
combinations include nickel-iron, cobalt-iron, and
nickel-cobalt-iron materials.
[0024] Filler material 14 is a non-magnetic layer and includes top
surface 14a. Filler material 14 isolates magnetic portion 12 in the
lateral directions of surfaces 12b, 12d. Filler material 14 is
derived from non-magnetic materials, such as oxide materials.
Examples of suitable oxide materials include aluminum oxide
(Al.sub.2O.sub.3), silica dioxide (SiO.sub.2), SiO.sub.xN.sub.y,
and combinations thereof. An example of a particularly suitable
material includes aluminum oxide.
[0025] Filler material 14 may have a thickness as individual needs
may require, for example, where the thickness of filler material 14
is the distance between top surface 14a and top surface 8a of
underlying substrate 8. Preferably, filler material 14 has a
thickness less than the thickness of magnetic bit 12 to account for
the thickness of stop layer 16 (i.e., the thickness of magnetic bit
12 equals the combined thicknesses of filler material 14 and stop
layer 16).
[0026] Stop layer 16 is disposed on top surface 14a of filler
material 14 adjacent to surfaces 12b, 12d of magnetic portion 12.
Stop layer 16 includes top surface 16a and provides a means for
detecting the CMP endpoint for planarizing magnetic layer 10. This
provides an accurate control of the target thickness of magnetic
feature 10. Preferably stop layer 16 has a thickness between about
2-100 nm, and more preferably between about 2-10 nm, where the
thickness is the distance between top layers 16a of stop layer 16
and top layer 14a of filler material 14.
[0027] Stop layer 16 is non-magnetic, corrosion resistant, and has
high removal rate selectivity versus the magnetic alloys of
magnetic bit 12 and magnetic isolation materials of filler material
14 (i.e., relatively high abrasion resistance). By being
non-magnetic, stop layer 16 assists filler material 14 in
magnetically isolating magnetic portion 12 in the lateral
directions of surfaces 12b, 12d. Corrosion resistance is also
desired so that stop layer 16 withstands chemical attacks by CMP
slurries.
[0028] Preferably, the selectivities of the materials for stop
layer 16 versus the magnetic alloys of magnetic bit 12 and magnetic
isolation materials of filler material 14 are at least about
eighty-to-one. Examples of suitable materials for stop layer 16
include platinum, gold, chromium, ruthenium, diamond, tungsten,
SiC, SiO.sub.xN.sub.y, NiCu, and combinations thereof. An example
of a particularly suitable material for stop layer 16 is carbon.
Carbon is non-magnetic, corrosion resistant, and provides a high
selectivity versus materials for magnetic bit 12 and filler
material 14.
[0029] Stop layer 16 provides a means for accurately detecting the
endpoint of a CMP process, which may be accomplished in several
manners. First, the CMP endpoint may be detected based upon
measurable fluctuations in the motor current of a CMP apparatus
(not shown). These fluctuations are induced by changes in polishing
friction during a polishing process (i.e., changes in removal
rates), and correlate to the differences in removal rate
selectivities between the layers. Additionally, the CMP endpoint
may also be detected by changes in surface optical reflectivity and
changes in eddy currents induced through the layers. The detection
of the CMP endpoint through these techniques allows top surface 16a
and surface 12a to be evenly planarized for providing a smooth
surface for magnetic layer 10.
[0030] FIGS. 2A-2G are sectional views illustrating one embodiment
of a method of forming a magnetic recording medium according to the
present invention. FIG. 2A depicts portion 107 of a magnetic
recording medium, which is analogous to portion 7, prior to the
formation of magnetic layer 10. As illustrated, portion 107
includes underlying substrate 108 and magnetic layer 110 at an
initial stage of formation prior to the formation of discrete
magnetic bits and the additional of filler material by conventional
photolithography processes. Alternatively, bit-patterning processes
as described above may be used.
[0031] Whether by conventional photolithographic processes or
bit-patterning, discrete magnetic bits 112 are formed on substrate
108, as depicted in FIG. 2B. As shown, magnetic bit 112 has
dimensions defined by surfaces 112a-112d. Magnetic bit 112 has a
width defined by the distance between surfaces 112b, 112d.
[0032] As depicted in FIG. 2C, after magnetic bit 112 is formed,
non-magnetic material is deposited on top surface 108a of
underlying substrate 108 and magnetic bit 112 to form filler
material 114. After deposition, filler material 114 has a thickness
defined by the distance between top surface 114a of filler material
114 and top surface 108a of underlying substrate 108. Filler
material 114 also includes a step portion, noted by step surface
113b, formed over magnetic bit 112.
[0033] After filler material 114 is deposited, stop layer 116 is
formed by depositing material on top of filler material 114. This
is depicted in FIG. 2D. After deposition, stop layer 116 has a
thickness defined by the distance between top surface 116a of stop
layer 116 and top surface 114a of filler material 114. Stop layer
116 also includes a step portion, noted by step surface 116b,
formed over magnetic bit 112.
[0034] As previously mentioned, it is preferable that the combined
thicknesses of filler material 114 and stop layer 116 are generally
equal to the thickness of magnetic bit 112. Alternatively, the
combined thicknesses of filler material 114 and stop layer 116 may
be less than the thickness of magnetic bit 112. In this case, the
additional amount of magnetic bit 112 will be removed by the CMP
process. Moreover, it is noted that the combined thicknesses of
filler material 114 and stop layer 116 should not be greater than
the thickness of magnetic bit 112. This would prevent the CMP
process from planarizing magnetic layer 110 when stop layer 116 is
reached.
[0035] After stop layer 116 is formed, an additional layer of
non-magnetic material is deposited on top of stop layer 116, as
depicted in FIG. 2E to form excess layer 118. The thickness of
excess layer 118 is the distance between top surface 118a of excess
layer 118a and top surface 116a of stop layer 116. Excess layer 118
is incorporated to provide an adequate polishing time to remove the
step portions above magnetic bit 112, noted by step surfaces 114b,
116b.
[0036] Suitable materials for excess layer 118 include the suitable
materials described in FIG. 1 for filler material 14. Moreover, it
is desirable that the materials used for stop layer 116 have higher
removal rate selectivities versus the materials used for excess
layer 118. This allows the CMP process to remove excess layer 118
at a greater rate than stop layer 116. Generally, preferred
thicknesses of excess layer 118 provide an adequate polish time to
remove the step portions above magnetic bit 112.
[0037] After magnetic layer 110 as depicted in FIG. 2E is formed,
magnetic layer 110 is polished via a CMP process to planarize
magnetic layer 110 and expose magnetic bit 112. During the CMP
process, material is removed from excess layer 118 by a combination
of chemical etching and abrasion by the polishing pad of the CMP
apparatus (not shown). While the polishing pad removes the material
from excess layer 118, polishing friction is induced on the
polishing pad. This polishing friction corresponds to the material
removal rate and is measurable by the motor current of the CMP
apparatus.
[0038] Additionally, the CMP endpoint may further be detected by
changes in the surface optical reflectivities when excess layer 118
is removed and top surface 116a of stop layer 116 is exposed. The
surface optical reflectivity is measured for an entire wafer, by
laser or by normal light enhanced by optical fibers. The light is
directed to the surface being polished (i.e., excess layer 118),
reflects the light at a given angle based upon the material used
for excess layer 118. As excess layer 118 is removed by the CMP
apparatus, the reflectivity remains substantially unchanged.
However, when stop layer 116 is reached, the reflectivity changes
because of the differences in reflectivities between the materials
of stop layer 116 and excess layer 118. The CMP endpoint may
additionally be triggered when this change in surface optical
reflectivity is detected. Those skilled in the art will appreciate
and understand suitable systems for measuring the surface optical
reflectivity.
[0039] The CMP endpoint may also be detected by measuring changes
in electrical currents (i.e., eddy currents) induced through the
layers. The electrical currents are induced from the CMP slurry
through the layers of magnetic feature 110, and are detected by a
sensor (not shown) located below the wafer. As material is being
removed by polishing, the electrical currents correspondingly
change due to the drop in electrical resistance. As such, the rate
of change in the electrical currents detected correlate to the rate
of material removal. Therefore, when the rate of material removal
is substantially reduced (e.g., when stop layer 116 is reached),
the rate of change in the electrical current is also substantially
reduced. The CMP endpoint may additionally be triggered when the
rate of change in the electrical current are substantially reduced.
Those skilled in the art will appreciate and understand suitable
systems for inducing and measuring eddy currents.
[0040] Moreover, detecting the CMP endpoint by combinations of
these techniques further decreases the variations in detecting the
CMP endpoint. This provides greater accuracy in controlling the
thickness of magnetic layer 110.
[0041] FIG. 2F depicts magnetic layer 110 after a portion of excess
layer 118 has been removed such that step surface 116b of stop
layer 116 is exposed. At this point, because of the higher removal
rate selectivity of stop layer 116 versus excess layer 118,
friction induced on the polishing pad increases (i.e., removal rate
decreases). Nonetheless, the increased friction due to the
encounter of step surface 116b of step layer 116 does not trigger
the CMP endpoint detection. The step portion over magnetic bit 112
is relatively small compared to the overall size of magnetic layer
110. As such, the increase in the friction induced on the polishing
pad at this point is not great enough to trigger the CMP endpoint
detection.
[0042] Moreover, the surface optical reflectivity remains
substantially unchanged because excess layer 118 still remains in
the regions over top surface 116a of stop layer 116. The rates of
change in the electrical current are also not substantially reduced
by the reduction in the material removal rate imposed by top
surface 116b of stop layer 116. Removal of material by the CMP
process continues until top surface 116a of stop layer 116 is
reached. At this point, due to the high removal rate selectivity of
stop layer 116 versus excess layer 118, the increase in friction
induced on the polishing pad is high enough to trigger the CMP
endpoint detection.
[0043] Additionally, the surface optical reflectivity changes
because excess layer 118 is removed to expose stop layer 116.
Moreover, because the material removal rate is substantially
reduced at stop layer 116, the rate of change in the induced
electrical current is correspondingly reduced. These additional
techniques also provide signals for triggering the CMP endpoint
detection.
[0044] Through the use of stop layer 116, the CMP endpoint is
accurately detected, which minimizes thickness variations induced
by under-polishing and over-polishing. FIG. 2G depicts portion 107
with magnetic layer 110 after the CMP endpoint has been detected
and polishing has been stopped. The result is a smooth planar
surface defined by surface 112a of magnetic bit 112 and top surface
116a of stop layer 116. The thickness of magnetic layer 110 is also
accurately determined and may be consistently replicated through
this method. Subsequently, optional overlying layer(s) 9 may be
formed to provide desired electrical and mechanical properties.
[0045] By detecting the CMP endpoint through a stop layer, the
target thickness of bit patterned features is accurately controlled
and WIWNU is improved. This allows magnetic recording media to be
fabricated accurately and consistently.
[0046] The above description is presented to enable a person
skilled in the art to make and use the invention, and is provided
in the context of a particular application and its requirements.
Various modifications to the preferred embodiments will be readily
apparent to those skilled in the art, and the generic principles
defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the invention. Thus,
this invention is not intended to be limited to the embodiments
shown, but is to be accorded the widest scope consistent with the
principles and features disclosed herein. Finally, the entire
disclosure of the patents and publications referred in this
application are hereby incorporated herein by reference.
* * * * *